Introduction
If you have ever had a hard drive that needed professional recovery, or even researched “data recovery labs”, you have probably encountered the term ‘evaluation’.  While the actual process of evaluating a failed drive is different for different manufacturers of drives, or even for different models from the same manufacturer, they all follow some basic steps.

The Steps Involved
When your drive arrives in the lab, the first thing the recovery engineer will do is check-in your drive.  The make, model, serial and other information about the drive will be recorded. The engineer will then perform a basic physical inspection for possible damage to the case, and a visual inspection of the printed circuit board (PCB) looking for signs of heat damage, loose components, or obvious issues with the PCB.

If the physical inspection is normal, the drive in need of recovery is usually attached to a hardware based system that will attempt to communicate with the drive at its lowest levels.  Depending on the exact type of drive, there are standardized protocols used to communicate with hard drives at the physical level.  Most desktop and laptop computers will use the ATA (Advanced Technology Attachment) standards and command set.  This standard set of commands allows communications between hard drives and computers from different vendors.   Along with the ATA commands, different drive manufacturers can implement vendor specific commands for their particular drives.  While the ATA commands are primarily designed for transferring data and some basic diagnostics, the vendor specific commands allow more detailed diagnostics and repair of some issues a drive may have.

The hardware diagnostics tools used are able to send not only the ATA commands to the drive, but can send vendor specific commands to the drive. This allows the engineer to check the drive status for errors and see what individual elements of the ATA standard are supported by a specific drive among, other things.  If the drive initializes properly, the engineer can move onto more detailed tests that will determine which regions of the drive are reading normally and which aren’t.

If the drive does not initialize, the engineer will move the drive to the next level of evaluation, using a hardware device that can communicate with the drive’s service area – portions of the magnetic platters and possibly the ROM chip on the PCB (that are not accessible by the operating system or program). These areas contain the drives firmware code--the programs that actually allow the drive to function. 

The technician can evaluate if the heads are able to properly read the firmware, and this behavior can often be used to determine if the issue is corrupt firmware, or a deeper physical problem.

If the issue is diagnosed as physical, the drive will normally be moved to the cleanroom for a physical inspection of the heads and media as a final determination of the potential for a successful recovery.

At some point in the whole process the engineer should be able to develop a recovery plan for the drive.  It’s not uncommon during the evaluation phase that the engineer will determine it is in the best interests of your data to start cloning the good readable sectors of your drive to another drive, even before the actual problem is pinned down.  Cloning is a process where the data that is readable from the patient drive’s surface is copied to the same sectors on a known good hard drive. Cloning doesn’t care about files and directories, it only replicates the values of each byte from the patient drive to the same byte on the target drive. This commonly happens on drives that do not reliably initialize.  The logic behind this is that there will always be one time which is the last time the drive will start, If this time was it’s last, it best to get the data that is readable now before continuing with the evaluation which may require a restart of the drive.

Conclusion
The evaluation of a failing drive may take 15 minutes or it may take several days. But once the evaluation is done, the data recovery engineer should have a plan for recovery, and the company should communicate the results of the evaluation and firm quote of the cost of recovery for your approval.

Finding a data recovery company that has the ability to recover your data without outsourcing any part of the work is critical.  Be sure to ask the company if they have an onsite clearnroom and if all work will be done by employees of their company exclusively.  If the company you are considering cannot meet these requirements, keep looking.  Quite possibly their “free” evaluation could cost you your only shot at getting the data back.